The goal of the proposed research is to develop selective methods for organic synthesis with strained molecules and rhodium carbenoids. The proposed research involves development of stereoselective transformations of strained three-membered ring compounds. Modes of reactivity that will be explored will include Diels-Alder reactions, and tandem Ring expansion/Claisen rearrangments of allyl cycloprop-2-ene carboxylates. Of particular interest is the unusual ability of strained molecules to control the stereochemical outcome of such reactions. Another goal of the proposed research is to expand the scope of Rh-carbenoid chemistry. Of particular interest is the development of ligands that facilitate reactions of )-alkyldiazo compounds, which are susceptible to (R)- hydride elimination. With insight from computational studies, catalysts will be designed that can navigate away from undesired reaction pathways and provide desired products with maximum selectivity. Because Rh-carbeniods are critical to the synthesis of cyclopropenes and cyclopropanes, addressing the limitations of the chemistry of Rhcarbenes is integral to advancing all aims of this proposal. A final aspect of this program will be to develop general, stereoselective methods for the synthesis of medium ring trans-cycloalkenes. Also developed will be new stereospecific reaction chemistry that transfers the planar chirality of the alkene to newly created stereocenters in products. Reactions to be studied include transannular cyclization reactions, and a stereoselective protocol for synthesizing trans-1,2-diols. Applications will include the development of a unified approach to the synthesis of a family of pyrrolizidine alkaloids.